Priority is claimed with respect to the application No. 199 36 904.6 filed in Germany on Jul. 30, 1999, the disclosure of which is incorporated herein by reference.
The invention concerns a catheter, in particular for intravascular uses in the general sense. In the general sense as interpreted herein the term catheter is also intended to cover for example electrode lines which can be introduced through blood vessels into a heart, for cardiac pacemakers, ablation catheters and also guide wires. Guide wires serve in particular as an ancillary means for inserting catheters in the narrower sense or cardiac pacemaker electrode lines through blood vessels in the human body.
A large number of such catheters are known, for example ablation catheters and guide wires, which at the proximal end are provided with mechanical positioning or setting means in order to deflect the distal end into a desired direction, by suitable manual actuation of the setting means. In that way the guide wire can also be introduced manually through blood vessels involving angled configurations. The guide wire once introduced then serves as an ancillary means for the guided introduction of a catheter or an electrode line. In that case the catheter can be clipped in a portion-wise manner onto the guide wire. Alternatively the catheter can also be pushed over the guide wire. For that purpose such a catheter has a suitable lumen.
An ablation catheter which is controllable manually is known for example from U.S. Pat. No. 5,273,535. The catheter essentially comprises a gripping or handle element which goes into a catheter stem from which extends a flexible guide tube which terminates in a catheter tip with integrated electrode. Disposed at the end of the gripping element which is opposite to the catheter stem, is an electric line, by way of which the electrode is supplied with electrical energy.
Two draw wires which are secured to the tip of the catheter extend within the flexible guide tube. The draw wires are arranged in such a way that pulling on one draw wire or the other makes it possible to deflect the tip of the catheter in a first direction or a direction opposite to the first direction. The draw wires do not provide for the transmission of a pressure force. By virtue of deflection of the tip of the catheter and an additional rotary movement of the guide tube by means of the gripping element, the catheter can follow the curved configuration of a hollow organ in the body, without causing damage thereto.
The draw wires are movable alternately in a pulling mode by way of transmission means which are disposed in the gripping element and which are operated manually by a control element. The control element is here in the form of a control wheel. The transmission means convert the rotary movement of the control wheel into the pulling longitudinal movement for the draw wires. The transmission means comprise a shaft which is arranged stationarily and coaxially with respect to the control wheel and against which a respective draw wire bears from each of both sides. The two draw wires are secured to an apex point on the shaft. If now for example a rotary movement in the counterclockwise direction is effected at the control wheel, then the shaft also rotates in the counterclockwise direction and a wire is wound onto the shaft corresponding to the angle of rotation covered, and is thereby pulled. The other draw wire is correspondingly relieved of load. This involves a deflection movement of the tip of the catheter. Deflection in the opposite direction is produced in a similar manner by way of rotation of the control wheel in the clockwise direction. With this structure, the degree of deflection is established by the diameter of the shaft and is really slight by virtue of the structural boundary conditions involved.
Other manually controllable catheters are to be found in U.S. Pat. Nos. 5,254,088 and 5,364,351. Of those, U.S. Pat. No. 5,245,088 shows various alternative configurations of catheters, with a respective pair of control wires which are arranged in a lumen of the catheter so that it is possible to provide for lateral deflection of the distal end of the catheter by virtue of a relative movement of the control wires with respect to each other in their axial direction. The radial direction in which the deflection of the distal end of the catheter occurs can be adjusted by the control wires being rotated with respect to the rest of the catheter about a common longitudinal axis. Relative axial displacement of the control wires with respect to each other and rotation thereof with respect to the catheter casing can be effected by means of a hand control unit at the proximal end of the catheter.
Taking that state of the art as its basic starting point, the object of the invention is to provide a catheter which can be introduced more easily than known catheters in particular through blood vessels of the human body to a desired location, for example into a heart.
In accordance with the invention, that object is attained by a catheter having at least one sensor which is arranged at the distal end of the catheter and which is adapted to pick up a spacing signal dependent on the spacing of the sensor relative to the vessel wall, and control means which are connected to the sensor for taking over the spacing signal.
By virtue of the spacing signal being picked up directly at the distal end of the catheter, information about the position of the distal end of the catheter in for example a blood vessel is available at the control means without additional, for example extracorporal ancillary means. The corresponding spacing signal can be processed by virtue of the control means being of a suitable configuration to put it into any desired form and in particular can be used to control the deflection of the tip of the catheter, either manually or automatically. The invention therefore involves the realization of detecting the approach of the distal end of the catheter by sensor means and making available a suitable signal for controlling the deflection of the catheter, so that the distal end of the catheter upon approaching a vessel wall can be deflected in such a way that it moves away from the vessel wall.
In this connection, a particularly preferred catheter is one which is distinguished by actuators which are operatively connected to the control means and which are adapted to provide for deflection of the catheter, wherein the control means are adapted in response to a spacing signal from the sensors to generate a corresponding control signal for the actuators and pass it thereto in order to operate the actuators in such a way that the distal end of the catheter moves away from the vessel wall as a result of corresponding deflection by the actuators. Such a catheter enjoys the great advantage that with its distal end it maintains a spacing relative to the vessel walls, of its own accord, whenever possible, and therefore can be introduced into and passed through a blood vessel without complicated and intensive observation and manual control. The invention accordingly embraces the notion of combining a sensor for the spacing signal with suitable control means and actuators for deflection of the catheter to give an automatically operating system.
The actuators or the control means or both can in principle be arranged both at the distal end of the catheter and also at the proximal end thereof. For example piezoelectric actuators are suitable for the arrangement at the distal end.
In an alternative configuration of the invention a catheter can also be designed in such a way that the spacing signals detected by the sensor are displayed at the proximal end in order to simplify the known control of the catheter with manual setting means for deflection of the catheter. Accordingly a preferred catheter is also one which includes display means which are connected to the control means for actuation thereby.
Preferably, at least three sensors are arranged in a radially distributed array at the distal end of the catheter. In that way it is possible to obtain information about the direction of the approach of the catheter to a vessel wail and to counteract the approach movement by suitable operation of the actuators.
In addition, a preferred catheter is one whose sensor is an optical sensor or whose sensors include optical sensors. A particularly preferred alternative configuration of a catheter in that respect is one in which the sensor or sensors include light guides or optical fibers which end at the distal end of the catheter. In this case, the end of a light guide or optical fiber can itself serve as a sensor for light which impinges on the end of the optical fiber. Accordingly, a preferred catheter is one in which at least one of the optical fibers is adapted to receive light at the distal end of the catheter and transmit the received light to the control means. In that case, the received light represents the spacing signal. The catheter preferably has a further light guide or optical fiber which is adapted to output light at the distal end of the catheter and which preferably at the proximal end of the catheter is connected to a light source which outputs infrared light. The latter alternative configuration of the catheter is based on the realization that blood involves a transmission of about 90% in the infrared range between about 600 and 650 nm and is thus xe2x80x9ctransparentxe2x80x9d. In that way it is possible for infrared light to be caused to issue by way of the one optical fiber at the distal end of the catheter and for the strength of the infrared light reflected by the vessel walls to be returned as the spacing signal by way of other optical fibers to the proximal end of the catheter where either display values or control signals for corresponding actuators are derived from the spacing signal.
In connection with optical sensors, control means which are adapted to process optical signals are preferred.
As an alternative to the last-mentioned variant of the invention, it is also possible to provide control means which are adapted to process electrical signals. Accordingly alternatively preferred catheters are distinguished by a sensor or a plurality of sensors for outputting electrical signals. Such sensors can be capacitive proximity sensors which experience a change in their capacitance with an approach to a vessel wall. A spacing signal can then be derived from the attenuation of an electrical alternating current signal.
An alternatively preferred electrical sensor includes impedance detection means having at least two electrodes which are adapted to detect the impedance of blood flowing between the electrodes. Such a sensor makes use of the physical effect that, depending on the respective flow state, laminar or turbulent, which occurs according to the distance relative to the vessel wall, the blood involves a different level of conductance so that a spacing signal can be derived in that way.
A further alternative in respect of electrical sensors is represented by heatable thermistors whose electrical resistance varies with temperature. By virtue of the heating of the thermistors, the temperature thereof depends on how much heat is given off by the distal end of the catheter to the blood. That amount of heat however depends on the flow speed of the blood relative to the catheter. In that respect, the flow speed of the blood in the proximity of the vessel wall is lower than at a spacing from the vessel wall. Accordingly, the thermistor at a greater distance from the vessel wall is cooled to a greater degree so that the signal corresponding to the temperature of the thermistor can serve as a spacing signal.
In the case of a catheter provided with actuators and control means, the arrangement preferably has manual control means which are operatively connected to the actuators and which are designed in such a way that they permit a deflection of the catheter in a predeterminable fashion irrespective of the spacing signals which are passed from the sensors to the control means. In that way, automatic control of the catheter can be controlled by a manual control, in order for example in the case of vessel branchings to be able to specifically and targetedly predetermine a direction by hand.